Heat assisted magnetic recording (HAMR) technology for use in a data storage device involves use of a laser heating source to provide additional energy during the data writing process (e.g., as data is written to a magnetic media disk). The energy/heat source is typically implemented using a semiconductor laser diode chip bonded on a sub-mount chip which, when the laser diode and sub-mount are considered together after bonding, is referred to as a Chip-On-Sub-mount-Assembly or COSA. The COSA is then attached to a magnetic head slider and the light energy from the laser diode chip is guided to the air bearing surface of the slider through a waveguide disposed in the slider to heat up the magnetic media for writing.